This invention relates, in general, to semiconductor devices, and more particularly to monolithic microwave integrated circuits having multiple, vertically stacked components.
It is well known in the semiconductor art that gallium arsenide has many unique properties and characteristics which are desirable in various semiconductor devices. For instance, semiconductor devices capable of operating at relatively high frequencies may be fabricated using gallium arsenide. Additionally, gallium arsenide is known to have a relatively high resistivity and low capacitance as compared to silicon which has high capacitance and low resistivity. Therefore, increased leakage problems occur in silicon devices that are generally not encountered in devices employing gallium arsenide. It is also well known in the semiconductor art that monolithic devices have desirable characteristics and properties as opposed to hybrid devices. Monolithic devices have reduced parasitics as well as no bond wires. The absence of bond wires in monolithic devices allows for increased yields in fabrication.
Monolithic microwave integrated circuits are generally fabricated using horizontal technology. In this technology, semiconductor device structures are built adjacent to each other and interconnected. Although reliable integrated circuits may be fabricated using horizontal processes, increased amounts of chip surface area are required. The requirement of increased chip surface area, in turn, causes the monolithic microwave integrated circuits to be fairly substantial in size. Therefore, a vertical technology wherein semiconductor components are stacked would require less chip surface area and allow for monolithic microwave integrated circuits of a reduced size.